You can use NSString’s rangeOfCharacterFromSet method to search the string for whitespace and newlines:

// Trim leading whitespace and newlines.
NSCharacterSet *charSet = [NSCharacterSet whitespaceAndNewlineCharacterSet];
NSRange range           = [attString.string rangeOfCharacterFromSet:charSet];
while (range.length != 0 && range.location == 0)
{
    [attString replaceCharactersInRange:range
                             withString:@""];
    range = [attString.string rangeOfCharacterFromSet:charSet];
}

// Trim trailing whitespace and newlines.
range = [attString.string rangeOfCharacterFromSet:charSet
                                   		  options:NSBackwardsSearch];
while (range.length != 0 && NSMaxRange(range) == attString.length)
{
    [attString replaceCharactersInRange:range
                             withString:@""];
    range = [attString.string rangeOfCharacterFromSet:charSet
                                              options:NSBackwardsSearch];
}